1. Technical Field
The present invention relates to a rubber composition for coating a steel wire material and more particularly relates to a rubber composition for coating a steel wire material having initial adhesion strength and water resistant adhesion strength with respect to a steel wire material at or above conventional levels, while being compounded with a compound derived from a natural product.
2. Related Art
Generally, in pneumatic tires, carcass layers and belt layers reinforced by steel wire materials are formed from reinforced rubber sheets having a plurality of steel wires twisted together to form steel cords and a plurality of the steel cords laid out and coated with rubber. Additionally, bead cores are formed from a reinforced rubber compound body having single steel wires coated with rubber and a plurality of these coated wires bundled together. The rubber composition for coating a steel wire material used in these components must both have superior initial adhesion strength and water resistant adhesion strength with respect to the steel wire material.
Japanese Unexamined Patent Application No. H04-39340 proposes compounding a cresol resin, a partial condensate of hexamethylolmelaminepentamethyl ether, organic acid cobalt salt, and the like in order to improve both initial adhesion strength and water resistant adhesion strength with respect to a steel wire material. However, cresol resins and partial condensates of hexamethylolmelaminepentamethyl ether are petroleum-based materials and use of these is not preferable from a standpoint of environmental issues such as restrictions on carbon dioxide emissions that have been enacted in recent years. Replacing such materials with non-petroleum based materials (compounds derived from natural products) that have little impact on the environment is desired.
However, conventionally, compounds derived from natural products (adhesion aids) for use as rubber compounds for coating steel wire materials that have an effect of increasing both the initial adhesion strength and the water resistant adhesion strength thereof have not been discovered.